The Data-Over-Cable Service Interface Specification (DOCSIS) was established by cable television network operators to facilitate transporting data traffic, primarily Internet traffic, over existing community antenna television (CATV) networks. In addition to transporting data traffic, as well as television content signals over a CATV network, multiple services operators (MSO) also use their CATV network infrastructure for carrying voice, video on demand (VoD) and video conferencing traffic signals, among other types of traffic.
Based in part upon increasingly complex topologies of cable and fiber networks in deployed DOCSIS-compliant systems, the DOCSIS 3.0 specification has enhanced the capabilities of the headend with regard to locating specific devices in its network. The DOCSIS 3.0 media access control (MAC) and upper layer protocols interface (MULPI) spec introduces the concepts of MAC domain upstream service groups (or MD-US-SGs). An MD-US-SG refers to the set of upstream channels from the same MAC Domain that is reached by a single cable modem. In order to help the headend cable modem termination system (CMTS) isolate each individual modem to a particular MD-US-SG and resolve upstream ambiguity, the spec has made multiple changes to the way cable modems perform ranging and registration on DOCSIS 3.0 networks.
Upstream (US) ranging was modified in DOCSIS 3.0 to no longer depend on collection of upstream channel descriptors (UCDs) for determination of potential upstream channels to range on. The cable modem now builds a candidate upstream channel identification (UCID) hierarchical candidate list by randomly ordering the UCIDs contained in an upstream ambiguity resolution channel list contained in the MAC domain descriptor (MDD) message from the CMTS. If any of these UCIDs are stored in non-volatile memory as the last operational transmit channel set, then the cable modem can move such UCIDs to the front of the hierarchical candidate list. In addition if any UCIDs were sent in a ranging-response (RNG-RSP) message, a config file, or a dynamic channel change-request (DCC-REQ) then these UCIDs are added to the head of the hierarchical candidate list. (See MULPI 10.2.3.5 for details) The modem can then proceed to look for UCDs for any UCIDs in the hierarchical candidate list. Starting at the head of the hierarchical candidate list it will attempt to perform initial ranging. If this process fails the cable modem can repeat using the next UCID from its list. Once it succeeds the cable modem can continue upstream ambiguity resolution initial ranging as directed by the CMTS. Further details on the specified upstream ranging procedure can be found in the DOCSIS 2.0 and 3.0 specifications and the MULPI specification, each of which are hereby incorporated by reference.
Though much consideration was put into upstream ranging in DOCSIS 3.0, testing has identified that the changes with regard to the upstream channel candidate list can be limiting and can even cause outages in some situations.